Oh and btw you can simplify this snippet using our new time selecor that just launched few weeks ago:
{note}{zones=["UTC":0, "EST":-5, "PST":-7]}
Appointment date: {formdate: YYYY-MM-DD; name=date} at {formdate: hh:mma; name=time}
Timezone: {formmenu: name=timezone; cols=6; values={=keys(zones)}}
{endnote: trim=right}
Your appointment is set for {time: MMMM Do, YYYY [at] h:mma [(your time)]; at={=date} {=time}; pattern=YYYY-MM-DD hh:mma; shift={=zones[timezone]}h}